Transcript Water & the Fitness of the Environment

UNIT 1
Chapter 3: Water & the Fitness of Life
Chapter 5: The Structure & Function of Macromolecules
The Nature of Water
Water’s chemical properties make life
possible on Earth:
– water is a polar molecule
– organisms depend on the cohesion of water
molecules
– water moderates temperatures on Earth
– solid water (ice) floats
– water is an ALMOST universal solvent
Water is a Polar Molecule
Oxygen is a VERY electronegative atom
– region around oxygen is has a slight negative
charge; region around hydrogens has a slight
positive charge
One water molecule
can hydrogen bond
with up to 4 other
water molecules
Organisms Depends on the Cohesion of
Water Molecules
Hydrogen bonds are constantly being
broken and reformed
– the phenomenon of cohesion describes how
water molecules are held to one another
Water molecules also adhere to other
substances/surfaces
Surface tension makes
water behave as if covered
by a film
Water Moderates Temperatures on
Earth
Definitions:
– kinetic energy
– heat
– temperature
Heat is measured in units called calories
(cal)
– amount of heat necessary to raise one gram
of water by 1°C
The specific heat of a substance is the
amount of heat that needs to be
gained/lost to raise/lower it’s temperature
by 1°C
– water = 1
– ethyl alcohol = 0.6
– iron = 0.1
Bodies of water act to moderate air
temperatures
– ocean temperatures and coastal areas are
more stable than inland
Water requires a lot of heat to vaporize
– 580 calories required to vaporize 1g of water
– hydrogen bonds must be broken first
Evaporative cooling prevents water from
vaporizing too much or too quickly
Solid Water (ice) Floats
Ice is less dense than liquid water
– a volume of water expands ~109% as it
freezes
Water is an ALMOST Universal Solvent
The polarity of water makes it able to form
hydrogen bonds with charged and other
polar molecules
Water can interact with molecules that are
ionic or polar
– hydrophilic
Non-polar molecules are insoluble in water
and will not dissolve
– hydrophobic (ex. oil)
END
Most Macromolecules are Polymers

Three of the four macromolecules
(Carbohydrates, proteins, and nucleic acids…not
lipids) form chainlike structures called polymers
 Individual pieces, monomers, are joined to
create polymers
 Monomers joined by dehydration
(condensation) reaction
 Polymers disassembled by hydrolysis
Dehydration & Hydrolysis

Dehydration: one monomer provides a
hydrogen, the other provides a hydroxyl

Hydrolysis: water is used to “restore” a
hydrogen to one monomer and a hydroxyl
to the other

Common to the digestive process
Carbohydrates

Carbohydrates exist as monomers, dimers,
and polymers

Special names: monosaccharide, disaccharide,
polysaccharide

Monosaccharides are joined by
dehydration reactions


Bond created: glycosidic linkage
Polysaccharides are monosaccharides
joined by many glycosidic linkages

Polysaccharides perform storage and
structural roles
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
Starch is composed entirely of glucose
monomers
Plants store starch in plastids

Cellulose is stored in plants’ cell walls

Animals store glucose in the form of glycogen
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
Highly branched like amylopectin
Chitin is found in exoskeletons of arthropods
and cell walls of many fungi
Lipids

Lipids (fats) are not constructed of
monomers

Created from glycerol and fatty acids

Fatty acids are joined to glycerol by an
ester linkage

3 fatty acids + 1 glycerol = triglyceride

Fatty acids vary in the number of carbons
and the number of double bonds present
between carbons


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No double bonds = saturated
One double bond = unsaturated
More than one double bond = polyunsaturated

Phospholipids contain two fatty acids and
a phosphate group
END
Proteins

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Proteins are instrumental in virtually
everything an organism does
They are polymers constructed of amino
acid monomers

Combinations of 20 amino acids are joined to
form polypeptides

Amino acids are categorized based on
their properties

Amino acids are joined by dehydration
reactions and form peptide bonds

Polypeptide orientation:
Amino end = N-terminus
 Carboxyl end = C-terminus

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Protein function is based on it’s 3-D
shape, or conformation

Protein conformation has four levels
Primary: linear sequence of amino acids
 Secondary: a-helices and b-pleated sheets,
created by hydrogen bonding among polypeptide
backbone
 Tertiary: marked by hydrogen, ionic, and covalent
bonding between R-groups of amino acids
 Quaternary: occurs only when a protein is
constructed of more than one polypeptide

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Primary
Secondary
Tertiary
Quaternary
Nucleic Acids

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Nucleic acids, DNA (DeoxyriboNucleic
Acid) and RNA (RiboNucleic Acid), store
and transmit genetic information
DNA has the ability to replicate itself as
well as the ability to create RNA


RNA used to create proteins
Central Dogma: DNA  RNA  proteins

Nucleic acids are polymers of monomers
called nucleotides

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Nucleotides = nitrogenous base + phosphate
group + pentose (5 carbon) sugar
Nucleotides are joined by phosphodiester link
END